This invention relates generally to the field of electrical control of electrically energized soldering devices and, more particularly, to a computer processor for selecting, calibrating and controlling heat to the tip of a precision soldering iron.
Although aspects of the present invention may be applied to a variety of soldering systems, it is particularly applicable to selecting and controlling the heat at the tip of a soldering tool used for precision soldering of electrical and electronic joints, especially in the environment of heat sensitive electronic components. Solid state devices, including large scale integrated circuits known as computer and digital "chips" are examples of such heat sensitive devices.
A number of devices and systems for controlling the temperature of soldering devices have been proposed, including the above-identified prior application, Ser. No. 07/749,659, of the present inventor; however, there remain operational aspects which need improvement and additional features are desired that cannot be implemented in hardware circuitry. For example, in precision soldering of miniature circuitry, especially when the soldering joints are near heat sensitive components which can be destroyed by inadvertent overheating, precision control of the temperature at the tool tip is critical. This temperature control at the to-be-soldered junction, as well as in the adjacent circuit components, is not easily achieved using conventional soldering technology.
For example, while systems have been developed which allow the user to select a desired tip temperature using a dial or other user control, often times the actual tip temperature of the iron does not match the dial selected temperature. There could be a variety of reasons for this, including lack of calibration of the thermoelectrical characteristics of the heating device and temperature feedback measurement, lack of precision of analog temperature selection dials which are susceptible to parallax error when trying to match the index mark on the control knob to the temperature graduations, and absence of precision calibration of the apparatus to a known temperature standard over the entire thermal range. While the parallax error can be alleviated in devices that have a digital readout, equipment that is equipped with such readouts often does not have the precision calibration and feedback control needed to provide a reliable correspondence between the displayed selected temperature on the readout and the actual tip temperature of the soldering tool.
In those prior art devices which have calibration procedures, often times the difficulty and excessive time required for the calibration process detracts from optimum maintenance and precision of the equipment.
Still other shortcomings of existing soldering control equipment are the lack of security over the temperature settings and calibration parameters, inflexibility in the soldering control to adapt quickly to different soldering tips which are likely to have diverse thermoelectric properties, and the need for the station to quickly change from one to another of several pre-established temperature settings for soldering joints having scheduled, critical temperature set points. Other drawbacks of certain prior art equipment include the inability to retain in memory temperature settings and calibration constants generated from prior soldering procedures. Thus, for example, in a multi-temperature, multi-tip soldering procedure, it would be desirable to store the various control parameters overnight or between shifts to avoid resetting the instrument at the start of work each day or shift. Furthermore, it would be desirable to prevent others from changing these settings without proper authorization.